Retinitis pigmentosa is a genetic eye condition in which cells of the retina, which are responsible for translating light rays into images in the brain, gradually deteriorate.

People with the condition start to lose peripheral vision first, then find it harder to see at night until eventually their central vision is lost as well. According to the national statistics, about one in 4,000 people in the United States are affected by RP.

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The artificial retina, called the Argus II Retinal Prosthesis System, is the first implantable device to treat the condition and is approved for people over age 25 with advanced RP who can see some light.

The device consists of a panel of electrodes that are surgically implanted in the eye, and a pair of glasses with an attached camera. The camera sends images to the electrodes, essentially bypassing the damaged retina and tapping into the optic nerve that signals the brain to "see" images.

In the future, it may also be approved to treat other conditions such as macular degeneration, which causes loss of vision in the elderly and affects about 2 million Americans.

Dr. Robert Greenberg, Second Sight's chief executive, told the New York Times that eventually, the company would like to implant the electrodes directly into the brain's cortex to treat blindness from all causes.

"This new surgically implanted assistive device provides an option for patients who have lost their sight to RP -- for whom there have been no FDA-approved treatments," said Dr. Jeffrey Shuren, director of the FDA's Center for Devices and Radiological Health, in a statement. "The device may help adults with RP who have lost the ability to perceive shapes and movement to be more mobile and to perform day-to-day activities."

Some of the early patients testing the device said they could distinguish boundaries between objects and differentiate light from dark. Some could read large letters, while for others, being able to match sock colors and detect street curbs were more important for helping them to live more independently.

"Without the system, I wouldn't be able to see anything at all, and if you were in front of me and you moved left and right, I'm not going to realize any of this," Elias Konstantopolous, one of about 50 Americans and Europeans using the device in clinical trials, told the New York Times. "When you have nothing, this is something. It's a lot."

During the FDA review that included reports from 30 participants using the device, the agency found that most patients performed basic tasks, like touching a square in a white field, better with the Argus II than without it and that 19 of the participants experienced no adverse effects to the surgery.

Based on those results, the agency approved the Argus II as a humanitarian use device, meaning that it may help fewer than 4,000 people but that these patients have no other alternatives to treat their condition.

The Argus II is already available in Europe, and will be available at seven hospitals in New York, California, Texas, Maryland and Pennsylvania. As reported in HealthDay, it costs about $100,000 in Europe, with another $16,000 for the surgery to implant the electrodes. Second Sight believes that U.S. insurers will likely cover the cost of the device for patients who may not have other ways of treating their vision loss.